Amino acids, also called the building blocks of proteins, are compounds that perform a large number of essential functions in the body. They are needed for vital processes such as building proteins and synthesising hormones and neurotransmitters.
Some may also be taken in supplement form to naturally enhance sports performance or improve mood. They are categorised as essential, conditionally essential or non-essential, depending on various factors.
What are essential amino acids?
Amino acids are organic compounds made up of nitrogen, carbon, hydrogen and oxygen, together with a variable side chain group. Your body needs 20 different amino acids to grow and function properly. Although these 20 amino acids are important for your health, only nine are classified as essential. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
Essential amino acids cannot be synthesised by the body and must be obtained through diet. The best sources of essential amino acids are animal proteins such as meat, eggs and poultry. When you eat protein, it is broken down into amino acids, which are then used to help your body with various processes, such as building muscle and regulating immune function.
Conditionally essential amino acids
There are several non-essential amino acids that are categorised as conditionally essential. These are considered essential only under specific circumstances such as illness or stress. For example; although arginine is considered non-essential, your body cannot meet demands when fighting certain diseases such as cancer. Therefore, arginine must be supplemented through diet to support your body's needs in certain situations.
Their roles in your body
The 9 essential amino acids fulfil a number of important and diverse tasks in your body:
Phenylalanine is a precursor of the neurotransmitters tyrosine, dopamine, epinephrine and norepinephrine. It plays an essential role in the structure and function of proteins and enzymes and in the production of other amino acids.
Valine is one of the 3 branched-chain amino acids, meaning it has a branched chain with side branches. These side branches help enzymes use this amino acid a little easier than other amino acids. Valine helps with muscle growth and regeneration and is an important component of energy production.
Leucine: like valine, leucine is a branched-chain amino acid that is critical for protein synthesis and muscle recovery. It also helps regulate blood sugar levels, promotes wound healing and produces growth hormones.
Isoleucine is the last of the 3 branched-chain amino acids and is active in muscle metabolism and highly concentrated in muscle tissue. It is also important for energy production, immune function and the production of collagen and elastin.
Threonine is a main component of structural proteins such as collagen and elastin, which are important building blocks of skin and connective tissue. It also plays a role in fat metabolism and immune function.
Tryptophan: although it is often considered a substance that causes sleepiness, tryptophan has many other functions. It is needed to maintain proper nitrogen balance and is a precursor to serotonin, a neurotransmitter that regulates your appetite, sleep and mood.
Methionine plays an important role in metabolism and detoxification. It is also required for tissue growth and the absorption of zinc and selenium, minerals vital to your health.
Lysine plays an important role in protein synthesis, the production of hormones and enzymes and the absorption of calcium. It is also very important for energy production, immune function and the production of collagen and elastin.
Histidine is used to produce histamine, a neurotransmitter vital for immune response, digestion, sexual function and sleep-wake rhythm. It is essential for the maintenance of the myelin sheath, a layer of white, fatty substance that insulates nerve endings.
Health Benefits of Amino Acid Supplements
While essential amino acids can be found in a wide range of foods, taking concentrated doses in supplement form has been linked to several health benefits.
Can improve sleep and mood Tryptophan is needed for the production of serotonin, a chemical that acts as a neurotransmitter in your body. Serotonin is an essential regulator of mood, sleep and behaviour. Although low serotonin levels have been associated with depressed mood and sleep disturbance, several studies have shown that administering tryptophan can reduce the symptoms of depression, improve mood and promote sleep. A 19-day study of 60 elderly women found that 1 gram of tryptophan per day increased energy and happiness, compared to a placebo.
May help increase exercise performance The 3 branched-chain amino acids (Leucine, Isoleucine and Valine) are widely used to reduce fatigue, improve athletic performance and stimulate muscle recovery after exercise. In a study of 16 resistance-trained athletes, amino acid supplementation with branched-chain amino acids improved performance and muscle recovery and reduced muscle soreness, compared to a placebo. In addition, taking 4g of leucine per day for 12 weeks increased strength performance in untrained men, showing that non-athletes can also benefit from essential amino acids.
May Promote Weight Loss Some human and animal studies have shown that branched-chain amino acids may be effective in stimulating fat loss. For example, an 8-week study of 36 strength-training men found that supplementing with 14 grams of branched-chain amino acids per day significantly reduced body fat compared to whey protein or a sports drink. A study in rats showed that a diet containing 4% supplemental leucine reduced body weight and fat percentage. However, other studies examining the possible link between branched-chain amino acids and weight loss were inconsistent. More studies are needed to determine whether these amino acids can promote weight loss.
Foods containing all 9 essential amino acids are called complete proteins. Complete protein sources are meat, seafood, poultry, eggs and dairy products. Soya, quinoa and buckwheat are plant foods that contain all 9 essential amino acids, making them complete sources of protein.
Other plant-based sources of protein such as beans and nuts are considered incomplete because they lack one or more of the essential amino acids. However, if you follow a plant-based diet, you can still ensure a good intake of all essential amino acids as long as you eat a variety of plant-based proteins every day. For example; choosing a variety of incomplete proteins such as beans, nuts, seeds, whole grains and vegetables can ensure that your essential amino acid needs are met, even if you choose to exclude animal products from your diet.